# Python : Giving a custom cost matrix in CalcEMD2?

I am trying to create a custom cost matrix (cyclic array indices) for earth mover's distance calculation between regular / numpy arrays :

```
#Example input : PointA = [0,0,1,0], PointB = [1,0,0,0]
def earthMoversDistance(pointA, pointB):
#indices = range(len(pointA))
dataA = np.array([pointA]).T
dataB = np.array([pointB]).T
def cyclicCostMatrix(length):
halfLength = int(length/2)
base = np.abs(range(-halfLength, halfLength))
base = np.roll(base, -halfLength)
return np.array([np.roll(base, i) for i in xrange(length)])
costMatrix = cyclicCostMatrix(len(pointA))
def convertArrayToCVAMat(arr):
cva64 = cv.fromarray(arr.copy())
cva32 = cv.CreateMat(cva64.rows, cva64.cols, cv.CV_32FC1)
cv.Convert(cva64, cva32)
return cva32
cvaA = convertArrayToCVAMat(dataA)
cvaB = convertArrayToCVAMat(dataB)
cvaCost = convertArrayToCVAMat(costMatrix)
emd = cv.CalcEMD2(cvaA, cvaB, cv.CV_DIST_USER, cost_matrix = cvaCost)
return emd
```

However, I am getting the error:

```
cv2.error: Only one of cost matrix or distance function should be non-NULL in case of user-defined distance
```

While my code may not be perfect, I am clearly not giving a distance function to the method call. Is this a bug in the python wrapper or my mistake? I am using OpenCV 2.4.2 I believe (the one that is linked to in python(x,y) ).

Any help will be much appreciated.